According to Google Trends, but also according to Distrowatch, our own statistics here at OSNews and overall sense of the industry during 2006, Ubuntu has a big leap in mind share ahead of its competition (please note that we don't dare to say "market share", although we are pretty confident that it's the most used Linux desktop out there today). The second Fedora has a very small edge ahead of SuSe (while in US is a clear second), while Debian is following fourth. Mandrake+Mandriva (add both names on Google Trends and then sum the results) is clearly way below the previous four distros, but a clear 5th nonetheless. Last year Ubuntu was only a bit ahead of the other distros worldwide, but 2006 seems to have skyrocketed the distribution in the people's minds and computers.

From what I hear, Ubuntu's strength is in it's user friendliness. This isn't true. You still need to manually edit .conf files, etc..
There are some distributions where you never have to touch command line like SuSE and Mandriva. These distributions are a lot more noob friendly than Ubuntu. They have administrative tools that help you modify system settings. Ubuntu barely has gnome-system-tools. Then why is Ubuntu more friendly? It's all the advertising on the internet in forums and news sites. Timing is also a big factor. Ubuntu came out at a time where many people where really considering switching over to Linux. Even fedora is way more user friendly than Ubuntu.